Process for the preparation of lactams

ABSTRACT

This invention relates to a process for the production of lactams by catalytic rearrangement of cycloketoximes in the presence of oleum. More specifically the invention relates to improving yields of lactam while reducing undesirable by-product formation by use of three stages of rearrangement with correlated adjustment of reaction conditions in each stage. Critical variables in each stage include acid concentration, free SO3 concentration, percent oxime added, reaction temperature and extent of mixing. Normally, the oxime fed to the process contains up to 6 percent water.

United States Patent [191 Smith 1 Oct. 21, 1975 PROCESS FOR THEPREPARATION OF LACTAMS [75] Inventor: Joseph A. Smith, Richmond, Va.

[73] Assignee: Allied Chemical Corporation, New

York, N.Y.

[22] Filed: Nov. 13, 1974 [21] Appl. No.: 523,303

[52] US. Cl 260/239.3 A [51] Int. Cl. C07D 201/04 [58] Field of Search260/2393 A [56] References Cited UNITED STATES PATENTS 2,221,369 11/1940Cass 260/2393 A Primary ExaminerI-lenry R. Jiles Assistant ExaminerR0bert T. Bond Attorney, Agent, or FirmFred L. Kelly [57] ABSTRACT Thisinvention relates to a process for the production of lactams bycatalytic rearrangement of cycloketoximes in the presence of oleum. Morespecifically the invention relates to improving yields of lactam whilereducing undesirable by-product formation by use of three stages ofrearrangement with correlated adjustment of reaction conditions in eachstage. Critical variables in each stage include acid concentration, freeS0 concentration, percent oxime added, reaction temperature and extentof mixing. Normally, the oxime fed to the process contains up to 6percent water.

7 Claims, No Drawings PROCESS FOR THE PREPARATION OF LACTAMS BACKGROUNDOF THE INVENTION This invention relates to a process for the productionof lactams by catalytic rearrangement of ketoximes. It relates inparticular to a process for the production of lactams by catalyticrearrangement of cycloketoximes in the presence of oleum.

It is known that cyclic ketoximes, especially cyclohexanone oxime, canbe rearranged into the corresponding lactams by the action of acidreagents such as oleum, concentrated sulfuric acid or acetic anhyride.

It is also known that the rearrangement of cyclic ketoximes can becarried out at elevated temperatures of 200 to 450C. in the gaseousphase in the presence of solid catalysts. Strongly acid catalysts areused such as various phosphoric acids, alkali metal bisulfates or boricacid, in most cases applied to carriers.

US. Pat. No. 3,350,393, issued Oct. 31, 1967, involves convertingcyclohexanone oxime into caprolactam by contacting the oxime with asolid catalyst at 210 to 450C. and condensing caprolactam from theeffluent reaction gas. The process includes the steps of quenching thereaction gas with liquid caprolactam having a temperature at least C.below the temperature of the gas mixture leaving the reaction zone andcondensing caprolactam therefrom in a condensation zone by directcooling with a low boiling solvent, e.g., water.

US. Pat. No. 3,418,314, issued Dec. 24, 1968, discloses an improvedprocess for the production of lactams by molecular rearrangement of acycloalkanone oxime in gaseous phase in the presence of a solidaluminum-containing catalyst.

US. Pat. No. 3,437,655, issued Apr. 8, 1969, is based on the discoverythat cycloaliphatic ketoximes can be made to yield the correspondinglactams if the oxime is reacted as oxime hydrochloride with hydrogenchloride.

U.S. Pat. No. 3,503,958, issued Mar. 31, 1970, relates to the molecularrearrangement of oximes to lactams in the presence of analumino-silicate catalyst.

More recently, US. Pat. No. 3,553,204, issued Jan. 5, 1971, involves thecontinuous production of lactams from cyclic ketoximes using mineralacids as a catalyst and cycling oxime and acid by way of nozzles fromcontinuous mixers in lieu of using agitator vessels.

SUMMARY OF THE INVENTION This invention relates to an improved processfor the production of lactams by catalytic rearrangement ofcycloketoximes, for example, cyclohexanone oxime, in the presence ofoleum. By this process, the yield of lactam is improved and productionof undesirable byproducts is reduced. Moreover, oleum requirements aresignificantly reduced as compared with prior art processes.

The process of the present invention may be summarized as follows. Aprocess for the production of lactams by catalytic rearrangement ofcycloketoximes in the presence of oleum comprising:

a. continuously feeding a first portion of a cy-.

cloketoxime consisting of 60 to 80 parts by weight of cycloketoximehaving a water content of up to 6 weight percent to a first catalyticrearrangement zone containing a circulating reaction mass having asulfuric acid to lactam weight ratio of 1.33 to 1.80, a free 50;,content of 2.0 to 14.0 weight percent, and a temperature of 50 to 105C.,said reaction mass being circulated at a rate at least 20 times the rateof feeding said cycloketoxime to said first catalyticrearrangement zone;

b. continuously feeding oleum to said first catalytic reaction zone inamount sufficient to maintain a sulfuric acid to lactam weight ratio of1.33 to 1.80 in said zone, said oleum containing S0,, in amountsufficient to react with all of the water in the cycloketoxime andmaintain the free SOQcontent of the circulating reaction mass at 2.4 to14.0 weight percent;

c. continuously feeding a portion of the circulating reaction mass fromthe first catalytic rearrangement zone substantially equivalent to thefeed of cycloketoxime to said zone, to a second catalytic'rearrang'ementzone containing a circulating reaction mass having a sulfuric acid tolactam weight ratio of at least 1.14, preferably 1.14 to 1.31, a free $0content of at least 0.82, preferably 0.82 to 6.5 weight percent, and atemperature of to 100C., said reaction mass in said second catalyticrearrangement zone being circulated at a rate of least 20 times the rateof feeding to said second catalytic rearrangement zone said portion ofthe circulating reaction mass from said first catalytic rearrangementzone;

d. continuously feeding a second portion of the cycloketoxime consistingof 5 to 20 parts by weight of the cycloketoxime having a water contentof up to 6'weight percent to said second catalytic rearrangement zone;

e. continuously feeding a portion of the circulating reaction mass fromthe second catalytic rearrangement zone substantially equivalent to thefeedto said zone, to a third catalytic rearrangement zone containing acirculating reaction mass having a sulfuric acid to lactam'weight ratioof at least 1.00, preferably 1.00 to 1.13, and a free S0 content of atleast 0.40, preferably 0.40 to 4.0 weight percent, and a temperature of70 to 100C., said reaction mass in said third catalytic rearrangementzone being circulated at a rate at least 20 times the rate of feeding tosaid third catalytic rearrangement zone said portion of the circulatingreaction mass from said second catalytic rearrangement zone;

f. continuously feeding a third portion of the cycloketoxime consistingof 5 to 20 parts by weight of the cycloketoxime having a water contentof up to 6 weight percent to said third catalytic rearrangement zone;

g. continuously withdrawing a portion of the circulating reaction massfrom the third catalytic rearrangement zone substantially equivalent tothe feed to said zone; and 1 h. recovering lactam from the portion ofthe circulating reaction mass withdrawn from the third catalyticrearrangement zone.

For determination of the sulfuric acid to lactam weight ratio in saidthree catalytic rearrangement zones, the present is consideredequivalent to sul' furic acid, i.e., it is included in the calculationas sulfuric acid.

The residence time of the oxime in contact with the catalyst shouldamount to at least 3.0 to 10 seconds. A study of the reaction kineticsled to a decrease of reaction temperature from the normal prior arttemperature of about 110C. to preferably 70 to C. This.

lower temperature produces crude lactam of excellent color.

The process according to the invention is'suitable for rearrangingcycloalkanone oximes which have five to 12 carbon atoms in the ring tothe corresponding lactams. For example, cyclopentanone oxime,cyclohexanone oxime and methyl cyclohexanone oxime may be used. Whenhigher homologs of cyclohexanone oxime are converted, solvent might haveto be used.

DESCRIPTION OF THE PREFERRED EMBODIMENT Although the Beckmannrearrangement according to the invention is independent of the oximeused, the preferred embodiment is described in terms of the conversionof cyclohexanone oxime to e-caprolactam. The preferred process issummarized as follows:

A process for the production of caprolactam by catalytic rearrangementof cyclohexanone oxime in the presence of oleum comprising:

a. continuously feeding a first vportion of cyclohexanone oximeconsisting of 60 to 80 parts by weight of cyclohexanone oxime having awater content of 0.1 to 5 weight percent to a first catalyticrearrangement zone containing a circulating reaction mass having asulfuric acid to caprolactam weight ratio of 1.40 to ,1 .60, a free SO;content of 3.0 to 10.0 weight percent, and a temperature of 70 to 105C.,said reaction mass being circulated at a rate of 30 to 50 times the rateof feeding said cyclohexanone oxime to said first catalyticrearrangementzone;

b. continuously feeding oleum to said first catalytic reaction zone inamount sufficient to maintain a sulfuric acid to caprolactam weightratio of 1.40 to 1.60 in said zone, said oleum containing 80;, in amountsufficient to react with all of the water in the cyclohexanone oxime andmaintain the free 80;, content of the circulating reaction mass at 3.0to 10.0 weight percent;

0. continuously feeding a portion of the circulating reaction mass fromthe first catalytic rearrangement zone substantially equivalent to thefeed of cyclohexanone oxime to said zone, to a second catalyticrearrangement zone containing a circulating reaction mass having asulfuric acid to caprolactam weight ratio of 1.14 to 1.31, a free 80;,content of 0.82 to 6.5 weight percent, and a temperature of 70 to 100C.,said reaction mass in said second catalytic rearrangement zone beingcirculated at a rate 30 to 50 times the rate of feeding to said secondcatalytic rearrangement zone said portion of the circulating reactionmass from said first catalytic rearrangement zone;

d. continuously feeding a second portion of the cyclohexanone oximeconsisting of 5 to 20 parts by weight of the cyclohexanone oxime havinga water content of 0.1 to 5 weight percent to said secondcatalyticrearrangement zone;

e. continuously feeding a portion of the circulating reaction mass fromthe second catalytic rearrangement zone substantially equivalent to thefeed to said zone, to a third catalytic rearrangement zone containing acirculating-reaction mass having a sulfuric acid to caprolactam weightratio of 1.00 to 1.13, and a free S content of 0.40 to 4.0 weightpercent, and a temperature of 70 to 100C., said reaction mass in saidthird catalytic rearrangement zone being circulated at a rate 30 to 50times the rate of feeding to said third catalytic rearrangement zonesaid portion of the circulating reaction mass from said second catalyticrearrangement zone;

f. continuously feeding a third portion of the cyclohexanone oximeconsisting of 5 to parts by weight of the. cyclohexanone oxime having awater content of 0.1 to 5 weight percent to said third catalyticrearrangement zone; v

g. continuously withdrawing a portion of the circulating reaction massfrom the third catalytic rearrangement zone substantiallyequivalent tothe feed to said zone; and r h. recovering caprolactam from the portionof the circulating reaction mass withdrawn from the third catalyticrearrangement zone.

In accordance with said preferred process, the product acid/lactam ratiocan be reduced to 1.00 to 1.13 with excellent product qualityhThisadvantage results largely by knowledge of the effect of free S0 in thethree stages of rearrangement. It is desirable that all of the oleum beadded in the first stage of rearrangement, whereas the oxime must beadded in predetermined amounts to each'of the three stages. Resultsfurther indicate the need for using oleum having relatively high oleumstrength together with vigorous circulation in each of the three stagesof rearrangement. Other factors of importance are outlined hereinafter.

In the first reaction stage, the content of the oleum used is preferablyabove about 22-25 weight percent 80;, when the water content of theoxime is relatively high, e.g., 5 weight percent water in the oxime. Atanygiven acid/lactam ratio in the first stage of rearrangement, thiswill result in the presence of sufficient 80;; to increase lactamproduction and decrease formation of impurities. It isdesirable toprovide sufficient mixing intensity to destory localized hot spotscaused by high free 80;, in order to obtain the lowest possible amountof. impurities. The data indicate that optimum free $0 in thecirculating reaction mass in the first stage of rearrangement is in therange 3.5 to 6.5 weight percent 80,, when using a conventional in-linemixer.

The recovery of caprolactam from the portion of the circulating reactionmass withdrawn from the third catalytic rearrangement zone may beaccomplished by known procedures. Typically, the crude caprolactamrearrangement mass consisting essentialy of caprolactam and sulfuricacid is sent to a reactor system together with ammonia, water and asolvent such as toluene. The sulfuric acid is neutralized and thecaprolactam is simultaneously extracted from the ammonium sulfatesolution formed in this system. The product stream from saidneutralization step is sent to a phase separator where thesolvent-lactam phase is separated from the ammonium sulfate solutionphase. The ammonium sulfate phaseis extracted with fresh solvent toremove residual amounts of lactam. The ammonium sulfate solution is thensteam stripped to remove solvent and sent to an-ammonium sulfaterecovery unit. The solvent-lactam phase passes to a distillation towerwhere solvent is stripped from the lactam and the lactam is sent tostorage.

Desirably, the crude lactam is further purified, e.g., in accordancewith the purification process of US. Pat. No. 3,021,326, issued Feb. 13,1962, to Snider et al. As discussed in this patent a very high puritycaprolactam is required to assure good quality in polyamides producedtherefrom. A troublesome problem has been to separate certain oxidizableorganic impurities from the caprolactam. Presence of these inpurities isindicated by reaction of the lactam with potassium permanganate,solution. Quantitatively, the concentration of oxidizable impuritiescan be expressed as permanganate number, P.N., found by adding 1 ml. ofN/lOO KMnO aqueous solution to 50 mlof 0.1% caprolactam aqueoussolution; maintaining agitation for 250 seconds; and measuring opticaldensity of the resulting mixture in a cell of 5 cm. path with light of410 millimicron wavelength. This test shows the extent of oxidation ofimpurities by permanganate by measuring the intensity of yellowcoloration due to oxidation product formed. P.N. values in thisapplication are calculated by multiplying the measured opticaldensity'bylOO, optical density being defined as log (light transmittedby the solvent/light transmitted by the solution). Surprisingly, 1 havefound that at optimum conditions a crude lactam having P.N. of onlyabout 460 is produced using a 1.05 acid/lactam ratio in the last stageof the three stage rearrangement system of the present invention. Crudelactam having such P.N. values is easily purified by known procedures,such as the process of US. Pat. No. 3,021,326, to produce preferredlactam products having P.N. of 2 or less.

The following examples are specific embodiments of my process,illustrating my invention and the best mode contemplated by me ofcarrying it out. Partsand percentages are by weight unless otherwiseindicated.

EXAMPLE 1 About 72.5 parts per hour of cyclohexanone oxime containing4.9 percent water was continuously fed to a first catalyticrearrangement zone containing a circulating reaction mass having asulfuric acid to caprolactam weight ratio of 1.45 and a free 80,,content of 5.4 percent. Equipment consisted of an in-line mixing unitconnected in series with a flow meter, a heat exchanger and acirculation pump, arranged for circulating the reaction mass at a rate40 times the feed of cyclohexanone oxime. The equipment was sized toprovide a reaction time of about 0.5-5 hours. The oxime was pumped tothe in-line mixer in the circulating reaction mass. All equipment andpiping in contact with the reaction mass was 316 stainless steel. Thetemperature of the circulating reaction mass exit the heat exchanger wasmaintained at 80C. and the peak temperature in the reaction mass wasabout 102C. The sulfuric acid to caprolactam weight ratio of 1.45 in thecirculating reaction mass was maintained by continuously adding oleumcontaining 26 weight percent SO to the reaction mass. Exit the heatexchanger, a portion of the reaction mass equivalent to the feed theretowas continuously removed and fed to a second catalytic reaction zonehaving a sulfuric acid to caprolactam weight ratio of 1.20 and a free80;, content of about 3.2 percent. Equipment in the second catalyticrearrangement zone was similar to that used in the first catalyticrearrangement zone. About 15.1 parts per hour of'cyclohexanone oximecontaining 4.9 percent water was continuously pumped to the in-linemixer in the circulating reaction mass, which was circulated at a rate32 times the rate of feeding said portion of the reaction mass from thefirst catalytic rearrangement zone. The temperature of the circulatingreaction mass exit the heat exchanger was 80C. and the peak temperaturein the reaction mass was 86C. Exit the heat exchanger, a portion of thereaction mass equivalent to the feed thereto was continuously removedand fed to a third catalytic reaction zone having a sulfuric acid tocaprolactam weight ratio of 1.05 and a free 50;, content of about 1.6percent. Equipment in the third catalytic rearrangement zone wassimilar-to that used in the first and second catalytic rearrangement.zones. About 12.4 parts per hour of cyclohexanone oxime containing 4.9percent water was continuously pumped to the in-line mixer in thecirculating reaction mass, which was circulated at a rate 32 times therate of feeding said portion of the reaction mass from the secondcatalytic rearrangement zone. The temperature of the circulatingreaction mass exit the heat exchanger was C. and the peak temperature inthe reaction mass was C. Exit the heat exchanger, a portion of thereaction mass equivalent to the feed thereto was continuously withdrawn.The recovery of caprolactam from the portion of the circulating reactionmass withdrawn from the third catalytic rearrangement zone wasaccomplished by known processes in the manner described hereinabove. Thecrude lactam recovered had a P.N. of about 460. Yield of purified lactamwas 99.1 percent calculated on the cyclohexanone oxime entered.

EXAMPLE 2 The procedure of Example 1 was followed except that aconventional static mixer was used in the first catalytic rearrangementzone instead of the in-line mixer of Example 1. It was found that themaximum free S0 that could be tolerated using the static mixer was about4 weight percent S0 because the P.N. values increased very rapidly athigher free 80;, concentrations. Surprisingly, an increase in free S0 to1012 weight percent or more showed relatively little effect when thein-line mixer was used to provide a relatively high degree of mixingintensity in the first catalytic rearrangement zone. Other means forproviding vigorous mixing at the point of oxime addition gave similarresults.

EXAMPLE 3 The procedure of Example 1 was followed except that the peaktemperature in the first catalytic rearrangem'ent zone was varied overthe range 78-l05C. The P.N. peak temperature relationship was linearover the 78105C. temperature range with significantly lower P.N. valuesat the'lower temperatures.

EXAMPLE 4 The procedure of Example 1 was followed except that thereaction mass in the first catalytic rearrangement zone was circulatedat a.rate 266 times the feed of cyclohexanone oxime to said zone.Results indicated that the increased circulation rate gave nosignificant improvement in P.N. values oryield of product. However, acirculation rate at least 20 times the feed of oximeis desirable foradequate cooling of the reaction mixture in the heat exchanger.

EXAMPLE 5 The procedure of Example 1 was followed except that samples ofthe circulating reaction mass in the third catalytic rearrangement zonewere taken at various points in the circulating stream corresponding tovarious reaction times following addition of the oxime. It wasdetermined that the percent oxime in the reaction mass was reduced to0.08 percent within 1 1.4 seconds after addition of the oxime. Oxime inthe product stream was 0.07 percent.

I claim:

l. A process of the production of caprolactam by catalytic rearrangementof cyclohexanone oxime in the presence of oleum comprising:

a; continuously feeding a first portion of cyclohexanone oximeconsisting of 60 to 80 parts by weight of cyclohexanone oxime having awater content of up to 6 weight percent to a first catalyticrearrangement zone containing a circulating reaction mass having asulfuric acid to caprolactam weight ratio of 1.33 to 1.80, a free Scontent of 2.4 to 14.0 weight percent, and a temperature of 50? to'105C., said reaction mass being circulated at.a rate at least 20 timesthe rate of feeding said cyclohexanone oxime to said first catalyticrearrangement zone; 1

furic acid to caprolactam weight ratio of 1.40 to 1.60,

b. continuously feeding oleum to said first catalytic I reaction zone inamount sufficient to maintain a sulfuric acid to caprolactam weightratio of 1.33 to 1.80 in said zone, said oleum containing SO in amountsufficient to react with all of the water in the cyclohexanone oxime andmaintain the free 80;, content of the circulating reaction mass at 2.4

to 14.0 weight percent;

continuously feeding a portion of the circulating reaction mass from thefirst catalytic rearrangement zone substantially equivalent to the feedof cyclohexanone oxime to said zone, to a second catalytic rearrangementzone containing a circulating reaction mass having a sulfuric acid tocaprolactam weight ratio of at least 1.14, a free 80;, content of atleast 0.82 weight percent, and a temperature of 70 to 100C., saidreaction mass in said second catalytic rearrangement zone beingcirculated at a rate of at least times the rate of feeding to saidsecond catalytic rearrangement zone said portion of the circulatingreaction mass from said first catalytic rearrangement zone;

d. continuously feeding a second portion of the cyclohexanone oximeconsisting of 5 to 20 parts by weight of the cyclohexanone oxime havinga water content of up to 6 weight percent to said second catalyticrearrangement zone;

. continuously feeding a portion of the circulating reaction mass fromthe second catalytic rearrangement zone substantially equivalent to thefeed to said zone, to a third catalytic rearrangement zone containing acirculating reaction mass having a sulfuric acid to caprolactam weightratio of at least 1.00, and a free 80;, content of at least 0.40 weightpercent, and a temperature of 70 to 100C., said reaction mass in saidthird catalytic rearrangement zone being circulated at a rate at least20 times the rate of feeding to said third catalytic rearrangement zonesaid portion of the circulating reaction mass from said second catalyticrearrangement zone;

. continuously feeding a third portion of the cyclohexanone oximeconsisting of 5 to 20 parts by weight of the cyclohexanone oxime havinga water content of up to 6 weight percent to said third catalyticrearrangement zone;

g. continuously withdrawing a portion of the circulating reaction massfrom the third catalytic rearrangement zone substantially equivalent tothe feed to said zone; and

a free S0 content of 3.0'to 10.0 weight percent, and

a temperature of to 1'05C. and oleum is added in step (b) to maintainsaid sulfuric acid to caprolactam weight ratio of 1.40 to 1.60 and saidfree content of 3.0 to 10.0 weight percent. 4

. 4. The process of claim l wherein the circulating reaction mass in thesecond catalytic reaction zone has a sulfuric acid tocaprolactam weightratio of 1.14 to 1.31, and a free S 0 content of 0.82 to 6.5 weightpercent.

5. The process of claim 1 wherein the circulating reaction mass in thethird catalytic reaction zone has a sulfuric acid to caprolactam weightratio of 1.00 to 1.13, and a free 80;, content of 0.40 to 4.0 weightpercent.

6. The process of claim 1 wherein the cyclohexanone oxime added to eachof the three catalytic rearrangement zones is added with vigorousagitation.

7. A process for the production of caprolactam by catalyticrearrangement of cyclohexanone oxime in the presence of oleumcomprising:

a. continuously feeding a first portion of cyclohexanone oximeconsisting of 60 to 80 parts by weight of cyclohexanone oxime having awater content of 0.1 to 5 weight percent to a first catalyticrearrangement zone containing a circulating reaction mass havingasulfuric acid to caprolactam weight ratio of 1.40 to 1.60, a free S0content of 3.0 to 10.0 weight percent, and a temperature of 70 to 105C.,said reaction mass being circulated at a rate of 30 to 50 times the rateof feeding said cyclohexanone oxime to said first catalyticrearrangement zone;

b. continuously feeding oleum to said first catalytic reaction zone inamount sufficient to maintain a .sulfuric acid to caprolactam ,weightratio of 1.40 to 1.60 in said zone, said oleum containing 80;, in amountsufficient to react with all of the water in the cyclohexanone oxime andmaintain the free I 80:, content of the circulating reaction mass at 3.0

to 10.0 weight percent;

continuously feedinga portion of the circulating reaction mass from thefirst catalytic rearrangement zone substantially equivalent to the feedof cyclohexanone oxime to said zone, to a second catalytic rearrangementzone containing a circulating reaction mass having a sulfuric acid tocaprolactam weight ratio of 1.14 to 1.31, a free 80;, content of 0.82 to6.5 weight percent, and a temperature of 70 to C., said reaction mass insaid second catalytic rearrangement zone being circulated at a rate 30to 50 times the rate of feeding to said second catalytic rearrangementzone said portion of .the circulating reaction mass from said firstcatalytic rearrangement zone;

.d. continuously feeding a second portion of the cyclohexanone oximeconsisting of 5 to 20 parts by .weight of the cyclohexanone oxime havinga water content of 0.1 to weight percent to said second catalyticrearrangement zone;

. continuously feeding a portion of the circulating reaction mass fromthe second catalytic rearrangement zone substantially equivalent to thefeed to said zone, to a third catalytic rearrangement zone containing acirculating reaction mass having a sulfuric acid to caprolactam weightratio of 1.00 to 1.13, and a free 80;, content of 0.40 to 4.0 weightpercent, and a temperature of 70 to 100C., said reaction mass in saidthird catalytic rearrangement zone being circulated at a rate 30 to 50times the rate of feeding to said third catalytic rearrangement zonesaid portion of the circulating reaction mass from said second catalyticrearrangement catalytic rearrangement zone.

1. A PROCESS OF THE PRODUCTION OF CAPROLACTAM BY CATALYTIC REARRANGEMENTOF CYCLOHEXANONE OXIME IN THE PRESENCE OF OLEUM COMPRISING: A.CONTINUOUSLY FEEDING A FIRST PORTION OF CYCLOHEXANONE OXIME CONSISTINGOF 60 TO 80 PARTS BY WEIGHT OF CYCLOHEXANONE OXIME HAVING A WATERCONTENT OF UP TO 6 WEIGHT PERCENT TO A FIRST CATALYTIC REARRANGEMENTZONE CONTAINING A CIRCULTING REACTION MASS HAVING A SULFURIC ACID TOCAPROLACTAM WEIGHT RATIO OF 1.33 TO 1.80 A FREE SO3 CONTENT OF 2.4 TO14.0 WEIGHT PERCENT AND A TEMPERATURE OF 50* TO 105*C SAID REACTION MASSBEING CIRCULATED AT A RATE AT LEAST 20 TIMES THE RATE OF FEEDING SAIDCYCLOHEXANONE OXIME TO SAID FIRST CATALYTIC REARRANGEMENT ZONE, B.CONTINUOUSLY FEEDING OLEUM TO SAID FIRST CATAYTIC REACTION ZONE INAMOUNT SUFFICIENT TO MAINTAIN A SULFURIC ACID TO CAPROLACTAM WEIGHTRATIO OF 1.33 TO 1.80 IN SAID ZONE SAID OLEUM CONTAINING SO3 IN AMOUNTSUFFICIENT TO REACT WITH ALL OF THE WATER IN THE CYCLOHEXANONE OXIME ANDMAINTAIN THE FREE SO3 CONTENT OF THE CIRCULATING REACTION MASS AT 2.4 TO14.0 WEIGHT PERCENT C. CONTINUOUSLY FEEDING A PORTION OF THE CIRCLATINGREACTION MASS FROM THE FIRST CATAYTIC REARRANGEMENT ZONE SUBSTANTIALLYEQUIVALENT TO THE FEED OF CYCLOHEXANONE OXIME TO SAID ZONE TO A SECONDCATALYTIC REARRANGEMENT ZONE CONTAINING A CIRCULATING REACTION MASSHAVING A SULFURIC ACID TO CAPROLACTAM WEIGHT RATIO OF AT LEAAST 1.14 AFREE SO3 CONTENT OF AT LEAST 0.82 WEIGHT PERCENT AND A TEMPERATURE OF70* TO 100*C SAID REACTION MASS IN SAID SECOND CATALYTIC REARRANGEMENTZONE BEING CIRCULATED AT A RATE OF AT LEAST 20 TIMES THE RATE OF FEEDINGTO SAID SECOND CATALYTIC REARRANGEMENT ZONE SAID PORTION OF THECIRCULATING REACTION MASS FROM SAID FIRST CATALYTIC REARRANGEMENT ZONE,D. CONTINUOUSLY FEEDING A SECOND PORTION OF THE CYCLOHEXANONE OXIMECONTING OF 5 TO 20 PARTS BY WEIGHT OF THE CYCLOHEXANONE OXIME HAVING AWATER CONTENT OF UP TO 6 WEIGHT PERCENT TO SAID SECOND CATALYTICREARRANGEMENT ZONE, C. CONTINUOUSLY FEEDING A PORTION OF THE CIRCULATINGREACTION MASS FROM THE SECOND CATALYTIC REARRANGEMENT ZONE SUBSTANTIALLYEQUIVLENT TO THE FEED TO SAID ZONE TO A THIRD CATALYTIC REARRANGEMENTZONE CONTAINING A CIRCULATING REACTION MASS HAVING A SULFURIC ACID TOCAPROLACTAM WEIGHT RATIO OF AT LEAST 1.00 AND A FREE SO3 CONTENT OF ATLEAST 0.40 WEIGHT PERCENT AND A TEMPERATURE OF 70* TO 100*C SAIDREACTION MASS IN SAID THIRD CATALYTIC REAR RANGEMENT ZONE BEINGCIRCULATED AT A RATE AT LEAST 20 TIMES THE RATE OF FEEDING TO SAID THIRDCATALYTIC REARRANGEMENT ZONE SAID PORTION OF THE CIRCULATING REACTIONMASS FROM SAID SECOND CATALYTIC REARRANGEMENT ZONE F. CONTINUOUSLYFEEDING A THIRD PORTION OF THE CYCLOHEXANONE OXIME CONSISTING OF 5 TO 20PARTS BY WEIGHT OF THE CYCLOHEXANONE OXIME HAVING A WATER CONTENT OF UPTO 6 WEIGHT PERCENT TO SAID THIRD CATALYTIC REARRANGEMENT ZONE, G.CONTINUOUSLY WITHDRAWING A PORTION OF THE CIRCULATING REACTION MASS FROMTHE THIRD CATALYTIC REARRANGEMENT ZONE SUBSTANTIALLY EQUIVALENT TO THEFEED TO SAID ZONE AND H. RECOVERING CAPROLACTAM FROM THE PORTION OF THECIRCULATING REACTION MASS WITHDRAWN FROM THE THIRD CATALYTICREARRANGEMENT ZONE.
 2. The process of claim 1 wherein the residence timeof the cyclohexanone oxime in contact with the oleum catalyst is atleast 3-10 seconds at 70* to 100*C.
 3. The process of claim 1 whereinthe circulating reaction mass in the first catalytic reaction zone has asulfuric acid to caprolactam weight ratio of 1.40 to 1.60, a free SO3content of 3.0 to 10.0 weight percent, and a temperature of 70* to105*C. and oleum is added in step (b) to maintain said sulfuric acid tocaprolactam weight ratio of 1.40 to 1.60 and said free SO3 content of3.0 to 10.0 weight percent.
 4. The process of claim 1 wherein thecirculating reaction mass in the second catalytic reaction zone has asulfuric acid to caprolactam weight ratio of 1.14 to 1.31, and a freeSO3 content of 0.82 to 6.5 weight percent.
 5. The process of claim 1wherein the circulating reaction mass in the third catalytic reactionzone has a sulfuric acid to caprolactam weight ratio of 1.00 to 1.13,and a free SO3 content of 0.40 to 4.0 weight percent.
 6. The process ofclaim 1 wherein the cyclohexanone oxime added to each of the threecatalytic rearrangement zones is added with vigorous agitation.
 7. Aprocess for the production of caprolactam by catalytic rearrangement ofcyclohexanone oxime in the presence of oleum comprising: a. continuouslyfeeding a first portion of cyclohexanone oxime consisting of 60 to 80parts by weight of cyclohexanone oxime having a water content of 0.1 to5 weight percent to a first catalytic rearrangement zone containing acirculating reaction mass having a sulfuric acid to caprolactam weightratio of 1.40 to 1.60, a free SO3 content of 3.0 to 10.0 weight percent,and a temperature of 70* to 105*C., said reaction mass being circulatedat a rate of 30 to 50 times the rate of feeding said cyclohexanone oximeto said first catalytic rearrangement zone; b. continuously feedingoleum to said first catalytic reaction zone in amount sufficient tomAintain a sulfuric acid to caprolactam weight ratio of 1.40 to 1.60 insaid zone, said oleum containing SO3 in amount sufficient to react withall of the water in the cyclohexanone oxime and maintain the free SO3content of the circulating reaction mass at 3.0 to 10.0 weight percent;c. continuously feeding a portion of the circulating reaction mass fromthe first catalytic rearrangement zone substantially equivalent to thefeed of cyclohexanone oxime to said zone, to a second catalyticrearrangement zone containing a circulating reaction mass having asulfuric acid to caprolactam weight ratio of 1.14 to 1.31, a free SO3content of 0.82 to 6.5 weight percent, and a temperature of 70* to100*C., said reaction mass in said second catalytic rearrangement zonebeing circulated at a rate 30 to 50 times the rate of feeding to saidsecond catalytic rearrangement zone said portion of the circulatingreaction mass from said first catalytic rearrangement zone; d.continuously feeding a second portion of the cyclohexanone oximeconsisting of 5 to 20 parts by weight of the cyclohexanone oxime havinga water content of 0.1 to 5 weight percent to said second catalyticrearrangement zone; e. continuously feeding a portion of the circulatingreaction mass from the second catalytic rearrangement zone substantiallyequivalent to the feed to said zone, to a third catalytic rearrangementzone containing a circulating reaction mass having a sulfuric acid tocaprolactam weight ratio of 1.00 to 1.13, and a free SO3 content of 0.40to 4.0 weight percent, and a temperature of 70* to 100*C., said reactionmass in said third catalytic rearrangement zone being circulated at arate 30 to 50 times the rate of feeding to said third catalyticrearrangement zone said portion of the circulating reaction mass fromsaid second catalytic rearrangement zone; f. continuously feeding athird portion of the cyclohexanone oxime consisting of 5 to 20 parts byweight of the cyclohexanone oxime having a water content of 0.1 to 5weight percent to said third catalytic rearrangement zone; g.continuously withdrawing a portion of the circulating reaction mass fromthe third catalytic rearrangement zone substantially equivalent to thefeed to said zone; and h. recovering caprolactam from the portion of thecirculating reaction mass withdrawn from the third catalyticrearrangement zone.